Unsurprisingly, there's a ton of heterogeneity which means it's easy to violate your statistical assumptions (i.i.d. being more important than normality here, I think) and so you get a lot of false positives. It's similar to the brain imaging issue: the assumption of spatial locality and Gaussianness is not really true and drives a lot of false-positive _p_-value inflation. There are really quite a lot of problems with animal studies, so it's not a surprise that they wipe out spectacularly when transferring to human.
I keep a list of systematic reviews & meta-analyses I run across at https://www.gwern.net/DNB-FAQ#fn95 One of the most impressive ones, I think, are sepsis treatments: ~150 sepsis treatment experiments in humans based on mouse/rat experiments, and all of them failed: "Genomic responses in mouse models poorly mimic human inflammatory diseases", Seok et al 2013 http://www.pnas.org/content/110/9/3507.full.html
"This kind of mouse we raised under these conditions, and we changed nothing, but they varied in these ways over time"
I often wonder whether the variables we check against are actually as independent and subject to the central limit theorem as we assume.